The present invention relates to the destruction of toxic substances such as organic compounds and microbial species in the process of purification or disinfection of aqueous and other environments.
Various undesirable compounds, such as heavy organic molecular compounds and microbial species, are often carried in waste water or other effluents, soils or other matrix environments, in which they may prove toxic in subsequent uses of the carrier material. One known process for sterilizing or disinfecting the carriers of these compounds is through irradiation with ultraviolet (UV) radiation. Most chemical bonds in organic toxins are broken under the action of the ultraviolet radiation through photodissociation. A particular substance will have a characteristic photodissociation curve associated with it specifying the energies of UV radiation for which the particular substance will undergo photodissociation. For effective photodissociation it is necessary that the UV radiation have the particular energy or energies which fall within the photodissociation curve of the substance of interest. For most organic toxins of interest here the photodissociation curves are greatest (indicating the greatest likelihood of dissociation) in the range of 175 to 300 nanometers (nm).
Most dissociation curves of interest have an effective range which can include many discrete UV emission energies (so-called emission "lines"). For effective destruction of the undesirable compounds it is not enough that the UV energies fall in the applicable range. Another necessary condition is that the radiation have a sufficient intensity. The necessary intensity depends on the photodissociation cross sections for the undesirable compounds and their concentrations in the carrier medium.
There is also a problem in effective destruction of toxic compounds in that the photodissociation process for a given compound may produce by-products which are themselves toxic and which must undergo further photodissociation until non-toxic end-products result. In other words a cascade of consequent UV photodissociation actions has to be applied to the original toxins and to the possibly toxic byproducts of the UV actions until the final byproducts are reduced to safe substances.
Typical UV sources generate only a relatively few intense UV emission lines falling in this energy range. These relatively few intense lines do not generally fall within the peak absorption range for all of the toxic compounds and their photodissociation byproducts occurring in a typical specimen.
Direct UV destruction of toxic compounds has not been employed in the prior art, which instead has relied on UV excitation of known intermediate additives such as ozone or peroxides.